Hardening alloy steels



Patented Mar. 21, 1933 UNITED STATES PATENT OFFICE HUBER'I. SUTTON,ARTHUR JOHN SIDERY, AND BENJAMIN EVANS, OF SOUTH.

' FARN BOROUGH, ENGLAND HARDENING ALLOY STEELS No Drawing. Applicationfiled November 18, 1930, Serial No. 496,559, and in Great BritainDecember This invention relates to improvements in surface-hardening orcase-hardening alloy steels by nitrogenization, by subjecting the alloysteel in a heated state to the action of ammonia. gas or other substancewhich gives off nitrogen.

It is known that a limited number of alloy steels, such as thosecontaining carbon, aluminium and separately or in any desired 0combination silicon, manganese, nickel, chromium, molybdenum, tungsten,vanadium, ti-

tanium or zirconium can be case-hardened to an extraordinary hardness,without appreciable distortion, by nitrogenization at a temperature notexceeding about 580 degrees Cent, the element which causes the alloysteel to become case-hardened being disseminated throughout the mass ofthe alloy steel.

It is also known that a limited number of 0 alloy steels, such as thosecontaining aluminium and vanadium can be case-hardened to anextraordinary hardness by nitrogenization at a temperature not exceedingabout 580 (3., the element which causes the alloy steel to becomecase-hardened, instead of be ing disseminated throughout the mass of thealloy steel, being concentrated in the surface layer. In the knownmethods the hardening element has been alloyed with the surface of thealloy steel by a high heat-treatment, which is separate from and'isfollowed by the nitrogenization heat-treatment. The known alloyingheat-treatment, besides being uneconomical, is of disadvantage in beingliable to distort the shape of manufactured articles to be casehardened.

The present invention prevents distortion of the basis metal by applyinthe element (which acts as an agent in t e hardening 40 process) as acoating to the surface of the alloy steel, by a cold process.

The improved process enables a specially tough and tenacious case to beobtained, and

' generally enables a high value of hardness and a greater depth of caseto be obtained than with the known process.

The present invention possesses the economical advantage of avoiding thenecessity of excessive heat-treatment of the basis metal prior tonitrogenization, while allowing the core of the basis metal to be of acharacter best suited for special purposes of strength, etc., withoutregard to suitability for nitrogenization.

In carrying out the invention, there is a plied to the surface of thealloy steel tocase-hardened while cold a film or coating ofcopper,silver, platinum, arsenic or cobalt, or any combination thereof, thecoating being porous and thin enough to permit penetration of nitrogento the alloy steel and serving as a nitride promoting agent to aid orcause the surface layer of the alloy steel to take up nitrogen and tobecome exceptionally hard when heated; the alloy steel is heated; andthe heated coated alloy steel is subjected to the action of nitrogen ora substance which gives off nitrogen. Some metals are not suitable ascoatings for the purpose of the present invention, for example, nickel,cadmium, zinc and tin.

The most suitable temperature to which the coated alloy steel should beheated varies according to the alloy steel, but generally speaking lieswithin the range 450 to 650 degrees Cent.

Immediately prior to receiving the coating, the alloy steel preferablyis cleaned.

The coating can be produced on the alloy" steel by any convenient methodsuch as electro-deposition, or spraying, or chemical displacement froman aqueous solution. When the coatingis sprayed on, it may be thickerthan when it is electro-deposited. In any event, the coating must bethin enough to permit penetration of the nitrogen to the alloy steel.When the coating is sprayed on a coating of the order of 0.0015 inch inthickness is suitable. When the coating is electro-deposited, orobtained by chemical displacement from an aqueous solution, a coating ofthe order of 0.00001 inch in thickness is suitable.

when electro-deposited, tends to prevent decarburizati'on, which is ofimportance in obtaining a highly tenacious layer.

1 It is believed that the coating, for example The invention isapplicable, for' example, to chroniium'steels, nickel-chromium steels, v

nickel-chromium-tungsten steels, aluminiumchromium steels,alumlnium-chromlum-molybdenum steels, high manganese steels,chromium-nickel manga-nese steels, silicon-chromium steels andchromium-molybdenum steels. Alloy steels containing from about 1 to 20per cent of chromium can'betreated.

By the described process a case having a thickness of the order of 0.005inch to 0.03 inch may be obtained, according, inter alia, to the natureof the alloy steel treated, and the duration and temperature oftreatment.

As an example of the use of a copper coating :An alloy steel containingabout 14 per cent of nickel, about 14 per cent of chromium, about 2 percent of tungsten and about 0.36 per cent of carbon is cleaned byimmersion for a few minutes in dilute sulphuric acid,

washed in water, plated with copper electrolytically, and subjected totreatment at a temperature of about 550 degrees Cent. for about 90 hoursin a current of ammonia gas. The ammonia gas may conveniently beobtained, for example, from liquid ammonia.

As another example of the use of a copper coating :An alloy steelcontaining about 8 per cent of nickel, about 20 per cent of chromium andabout 0.12 per cent of carbon is cleaned by immersion for a few minutesin dilute sulphuric acid, washed in water, plated with copperelectrolytically, and subjected to treatment at a temperature of about500 degrees Cent. for about 90 hours in a current of ammonia gas.

As a further example of the use of a copper coating :--An alloy steelcontaining about 5. per cent of manganese, about 12 per cent of nickel,about 3.5 per cent of chromium and about 0.5 per cent of carbon iscleaned by immersion for a few minutes in dilute sulphuric acid, washedin'water, plated with copper electrolytically, and subjected totreatment at a temperature of about 550 degrees Cent. for about 90 hoursin a current of ammonia gas.

As another example of the use of a copper coating :-An alloy steelcontaining about 1 per cent of chromium, about 0.2 per cent ofmolybdenum, about 0.4 per cent of manganese and about 0.3 per cent ofcarbon is cleaned by immersion for a few minutes in dilute sulphuricacid, washed in water, plated with copper electrolytically and subjectedto treatment at a temperature of about 550 degrees Cent. for about 90.hours in a current of -2fper cent of tungsten and about 0.36 per centcarbon is given a sprayed coating of cop- I per, and is afterwardssubjected to treatment at a temperature of about 550 degrees Gent.

for about 90 hours in a current of ammonia By way of comparing thealready known process with the present process, the following examplesmay be mentioned :-Experiments, carried out at a temperature of about500 degrees Cent. have shown that when applied to steel containing about0.14 per cent of carbon, about 8 per cent of nickel, and about 17 percent of chromium, the already known process gives no commercially usefulincrease in hardness; whereas the improved process using a coppercoating gives a considerably increased hardness, at least equal to andin some cases greater than that given by the in a current of ammoniagas, a higher value of hardness and a greater depth of case can beobtained where a coating of copper or other suitable metal or metalloidis present accordingto the improved process, than can be obtainedwithout said coating according to the known process, under conditionsotherwise similar. As an example of the use of a silver coatmg steelcontaining about 13 per cent of chromlum, about 0.25 per cent of carbonand up to about 0.3 per cent of nickel may be coated with silver, forexample by electro-deposition or by spraying, and then subjected totreatment at a temperature of about 500 degrees Cent. for about 90 hoursin a current of ammonia gas.

As another example of the use of a silver coating :'An alloy steelcontaining about 13 per cent of manganese and about 1.0 per cent ofcarbon may be coated with silver, for example by electro-deposition, andthen subected to treatment'at a temperature of about 500 degrees Gent.for about 90 hours in a current of ammonia gas.

As. an example of the use of a platinum coating :an alloy steelcontaining about 8 per cent of nickel, about 17 per cent of chromium andabout 0.14 per cent of carbon; or about 2 per' cent of nickel, about 18per cent of chromium and about.0.2 percent of carbon; may be coated withplatinum, for instance by electro-deposition, and then subjected totreatment at a temperature of about 500 degrees Cent. for about 90 hoursin a current of ammonia gas.

As an example of the use of an arsenic coating:An alloy steel containingabout 8 per cent of nickel, about 18 per cent of chromium and 0.14 percent of carbon may be coated with arsenic, for example byelectro-deposition or by immersion in a suitable solution, and thensubjected to treatment at a temperature of about 500 degrees Cent. forabout 90 hours in a current of ammonia gas. A suitable solution for usewhen steel is to be coated with arsenic by ordinary immersion consistsof 6 grams arsenic trioxide in 100 cc. concentrated hydrochloric acid,the bath being worked at about 60 degrees Cent. The article is immersedin the bath for about 2 minutes. When it is desired to deposit thecoating ele'ctrolytically an electrolyte consisting of an aqueoussolution containing about'4 per cent of arsenic trioxide and about 10per cent of sodium cyanide may be employed.

As an example of the use of a cobalt coating, an alloy steel containingabout 8 per cent of nickel, about 20 per cent of chromium and about 0.12per centof carbon may be coated with cobalt, for instance byelectro-deposition, and then subjected to treatment at a temperature ofabout 500 degrees Cent. for about 90 hours in a current of ammonia gas.

Although 90 hours has been referred to as the duration of treatment inthe above examples, the duration of treatment may be considerablyreduced, say to not less than 4 hours, depending upon the thickness ofcase required.

In general, the alloy steelto be treated may,

be cleaned by immersion for a few minutes in dilute sulphuric acid andwashing in water. a

When using ammonia gas, which gives off nitrogen in a highly activestate, the amount of dissociation of the gas should preferably berestricted within limits, say to about 20 to 40 per cent dissociation.The gas should preferably be supplied in a dry state for example bybeing passed through a tube containing quicklime.

The apparatus for carrying'out the improved process may consist of aheated chamber, in which the articles of alloy steel after being coatedare supported or suspended in such a manner as to permit of freecirculation of the gas around the articles, means for regulating thetemperature of the chamber, means for regulating the flow of ammonia gasinto the chamber, and means for leading the gaseous mixture ofi from thechamber. I

In any of the above examples, after. being heated to the suitabletemperature for a few of the above mentioned hours in the aII1.--

perature for the remainder of the abovementioned hours in the current ofammonia gas.

Instead of using ammonia gas as above regen may be employed.

What we claim is 1. Case-hardening an alloy steel by subjecting it tonitrogenization after coatingit while coldwitl'i a porous, thin,adherent film. of a nitride promoting agent of the group consisting ofcopper, silver, platinum, arsenic, cobalt, which permits penetration ofnitro en to the alloy steel. a

2. Troce'ss for hardening the surface of an alloy steel consisting inapplying to the surface while cold a porous, thin, adherent film of anitride promoting agentof the group consisting of copper, silver,platinum, arsenic, cobalt, which permits penetration of nitrogen to thealloy steel, heating the coated alloy steel, and subjecting the coatedand heated alloy steel to the actionof nitrogen or a substance whichgives off nitrogen.

3. Process for hardening the surface of an alloy steel containing fromabout 1 to 20 per cent of chromium, consisting in subjecting it tonitrogenization after coating it while cold with a porous, thin,adherent film of.a-

nitride promoting agent of the group consisting of copper, silver,platinum, arsenic, cobalt, which permits penetration of nitrogen to thealloy steel.

4. Process for hardening the surface of an alloy steel containing a highpercentage of manganese consisting in subjecting it to nitrogenizationafter coating it while cold with a porous, thin, adherent film of anitride promoting agent of the group consisting of copper, silver,platinum, arsenic, cobalt, which permits penetration of nitrogen to thealloy steel. 5. Case-hardening an alloy steel by subecting it tonitrogenization after coating'it while cold with a porous coating ofcopper which is thin enough to permit penetration of nitrogen to thealloysteel and acts as a nitride promoting agent in the hardeningprocess.

6. Cashardening an alloysteel by sub- I while cold with a porous coatingofarsenic which is thin enough to permit penetration of nitrogen'to thealloy steel and acts as a nitride promoting agent in the hardeningprocess. i J

8. Case-hardening an alloy steel bysubjecting it to nitrogenizationafter coating it 7 while cold by electrodeposition with a porous coatingof copper which is thin enough to permit penetration of nitrogen to thealloy Signed at London, England, this 6th day steel and acts as anitride promoting agent of November, 1930.

in the hardening process. HUBERT SUTTON.

9. Case-hardening an alloy steel by sub- ARTHUR JOHN SIDERY. jecting itto nitrogenization after coating it BENJAMIN EVANS. 70

1 hardening process.

permit penetration of nitrogen to the alloy while cold by spraying witha porous coatmg 12. Case-hardening an alloy steel by subthin enough topermit penetration of nitrogen while cold by electrodeposition with aporous coating of silver which is thin enough to permit penetration ofnitrogen to the alloy steel and acts as a nitride promoting agent in the10. Case-hardening an alloy steel by su jecting it to nitrogenizationafter coating it while cold by electrodeposition with a porous coatingof arsenic which is thin enough to steel and acts as a nitride promotingagent in the hardening process. I

11. Case-hardeningan alloy steel by subjecting it to nitrogenizationafter coating it of copper which is thin enoughto permit penetration ofnitrogen to the alloy steel and acts as a nitride promoting agent in thehardening process. 9O jecting it to nitrogenization after coating itwhile cold by chemical displacement by immersion in an aqueous solutionof a copper salt with a porous coating of copper which is to the alloysteel and acts as a nitride promoting agent in the hardening process.

35 porous film of copper which is thin enough 13. Case-hardeningarticles made of an alloy steel by coating them while cold with a topermit penetration of nitrogen to the alloy steel and acts as a nitridepromoting agent in the hardening process, and subjecting the coatedarticles to treatment at a temperature of about 450 to 650 Cent. forabout four to ninety hours in the presence of a substance which givesoff nitrogen.

14. Case-hardening articles made of an alloy steel by coating them whilecold with a porous film of copper which is thin enough to permitpenetration of nitrogen to the al 10y steel and acts as a nitridepromoting agent in the hardening process, subjecting o the coatedarticles to treatment at a tempera- I n5 ture of about 450 to 650 Cent.for some hours in the presence of a substance which gives 0E nitrogen,allowing the articles to cool to ordinary temperatures without being isremoved from the presence of the substance which gives ofl' nitrogen,and reheating the articles to about 450 to 650 Cent. for some hours.

15. Case-hardening'an alloy steel by sub- .0 jecting it tonitrogenization after coating it c while cold with a layer of a nitridepromoting agent of the group consisting of copper, silver, platinum,arsenic, cobalt, which is in a condition which permits penetration ofnitrogen to the alloy steel.

